It is common in food and drink packages to apply a printed polystyrene foam on the container and thereafter shrink the foam into contact with portions of the container in order that the label will conform to the contour of the container.
For example, in food packaging which is intended for reheating in a microwave oven, a tapered wall thermoformed plastic cup is filled with food and a sleeve is applied thereto about the periphery to serve as a label to identify the product and manufacturer and to serve as an insulator to permit handling of the cup and its contents after microwave heating. The foam label may be applied in the form of a previously made sleeve or by feeding a continuous sheet of web equal in width to the desired width of the label, cutting off a rectangular blank with a length sufficient to wrap fully around the cup and providing an overlapped seal to form a cylindrical sleeve equal in diameter to the maximum diameter of the cup. The sleeve may be attached by wrapping the blank about the cup utilizing heat seals, solvent seals, or adhesive. The cup with the sleeve thereon is then conveyed with or without rotation in an inverted position with the larger diameter facing downwardly through a heated oven which shrinks the foam label sleeve to the tapered contour of the cup and, in some instances, about a portion of the bottom of the cup. Such ovens conventionally employ strip infrared heaters extending along the side walls of the interior of the oven. Where the containers have large changes in diameter along their height, such as in a cup, in such arrangements, it is difficult to provide proper heat and to adjust the heat as may be required. Inasmuch as the cup is conveyed through the oven with the bottom up, the bottom is subjected to the upper part of the oven which is hotter. Also, the cylinder formed by the sleeve around the cup is further away from the lower portion of the cup due to the contoured shape. As a result, the foam material shrinks faster around the bottom of the cup entrapping air between the foam sleeve and the upper part of the cup. The effect of this is that the foam label does not fully conform to the contour of the cup and irregular air pockets are provided producing a wrinkled or puckered appearance.